This invention relates to electromagnetic circuits and is more particularly directed to a method of controlling the motion of an armature forming part of the circuit.
For many applications it has been found to be advantageous to monitor the motion of the solenoid armature in an electromagnetic circuit for energizing the holding magnet as a function of such a motion.
Electromagnetic circuits of the above-outlined type are used, for example, for controlling the intake and exhaust valves (hereafter also referred to collectively as cylinder valves) in internal combustion engines to obtain an adaptable control for the intake and exhaust of gases for the eventual purpose to optimally affect the operation based on requirements. The course of the control has a substantial effect on widely different parameters, for example, the conditions of the working medium in the intake region, in the work chamber and in the exhaust region as well as the conditions in the combustion chamber itself. Since internal combustion engines operate in a non-stationary manner under widely different operational conditions, a variable control of the cylinder valves is a desideratum. Such an electromagnetic circuit for cylinder valves is disclosed, for example, in German Patent No. 3,024,109.
A significant problem in the control of electromagnetic circuits of the above type involves the required timing accuracy which is needed in particular for the intake valves when the engine output is controlled. An accurate timing control is rendered difficult by manufacturing tolerances, wear appearing during operation as well as different operational conditions, for example, changing load requirements and operating frequencies, because these external influences may affect time-relevant parameters of the system.
A significant problem in electromagnetic circuits is the adherence (sticking) of the armature to the holding magnet. Such a phenomenon is caused mostly by eddy currents in the magnetic circuit. The sticking period depends from many different parameters such as the size of the air gap, the force exerted by the resetting means, usually formed of mechanical springs and from the counterpressure of the gases in case of cylinder valves. In addition to the unavoidable manufacturing tolerances in electromagnetically operated cylinder valves, the alternating gas counterpressures cause irregular fluctuations of the sticking period so that after a de-energization of the holding current, the motion start of the armature varies in an unpredictable manner. The stroke period too, as well as the energy losses and thus the energy to be supplied depend from the momentary operational conditions. By detecting the armature position during its motion between the two holding magnets, a compensation for the above-discussed influences would seem feasible. Such a compensation could be effected, for example, by a path sensor positioned between the two holding magnets. Such sensor can detect the moment--related to the control periods--when the armature moves past and can apply a signal to the control device so that the energization of the holding magnets may be affected by computer support. For use in electromagnetically controlled cylinder valves such a solution has value practically only in experimental engines. In the mass manufacture such an additional path sensor cannot be considered because of the high cost of the sensor itself and because of the required additional wiring of the contact locations which adversely affects the reliability of the entire system.
Tests have been previously conducted in an attempt to alleviate the problems with the aid of the available circuit components. This may be done, for example, by the evaluation of currents or voltages of the solenoids of the holding magnets by means of which the moment of impact of the armature on a holding magnet is detected (as disclosed, for example, in published European Application 0 264 706) or the moment of separation of the armature from the holding magnet is sensed. The velocities of the armature are, however, very low in the end position, so that even in case of a relatively good resolution of the signals representing such position, the time association which can be derived therefrom has not been found to be satisfactory. Accordingly, for improving such electromagnetic circuits, particularly to actuate cylinder valves, published European Application 0 405 189 proposes to improve the time accuracy by increasing the bias of the resetting means effective in the opening direction, and additional measures have been provided for changing the magnetic resistance in the magnetic circuit.